The proposed design is not intended as a commercial flow regulator to fill a wide variety of needs and a wide choice of flow rates in a single design. Rather it has special features to fit it to special aplications, such as use in a fountain dispenser for soft drinks to control the rate of flow of syrup and water. In such an application its limitations are minimal and its advantages over more conventional designs are considerable from the standpoints of utility, convenience and cost.
For example, the conventional regulator comprising a polished piston operating in a polished cylinder to open or close outlet holes in the cylinder wall is well designed to afford flow rates over a wide range of choice. However, only a narrow range of flow rates is required in a particular soft drink dispenser, perhaps plus or minus 10% from a standard rate for syrup, to afford some choice toward a sweeter or less sweet drink than standard. The proposed design affords the required range for such an application at low cost, without providing an unnecessarily wide choice at much higher cost.
The proposed design has the inlet and outlet fittings axially aligned with each other, for convenience in installation at any point in the dispensing system, while at the same time affording external adjustment of the flow rate without disturbing the connecting lines. Previous designs having the inlet and outlet fittings aligned with each other, and which were adjustable, required disconnection of a line for internal adjustment of the flow rate.
Adjustment of the flow rate is especially convenient in the proposed design by movement of the outlet fitting. A special compression gland, comprising an O-ring, nut and washers, maintains a seal against leakage during adjustment and affords firm locking of the outlet fitting when the comression nut is tightened. Compression of the O-ring causes a strong bond between the rubber O-ring and the metal stem of the outlet fitting and thus secures the adjustment. Such a convenient arrangement has not been found in the prior art. The inlet fitting is also adjustable in the proposed design to vary the flow rate, although care must be taken to keep the main body of the regulator oriented in a way to have the set screw accessible after adjustment in order to lock the fitting in place. Such care is not required with the compression gland, the nut being accessible regardless of how the regulator body is turned on its longitudinal axis.
A special problem attending the use of a plunger that moves in response to flow to partially close an outlet hole axially aligned with it, such as in this design, has been noted in the prior art -- namely, a force acting on a small area of the plunger, the force being equal to the product of the overall pressure drop across the regulator and the area of the outlet hole. This force is in addition to the force on the plunger due to flow and tends to decrease the flow rate below the rate desired as the pressure drop increases across the regulator, giving what is known in the art as negative regulation. One obvious solution is the use of a relatively large plunger and relatively small outlet hole to minimize the force due to overall pressure drop compared to that due to flow. One previous design, using a large diaphragm instead of a plunger, did just this. Such a solution, however, is far from ideal if compactness for a given flow rate is important.
In the proposed design a unique solution to this problem has been found that permits use of a relatively small plunger and relatively large outlet hole. The plunger stem is shaped, for a particular flow rate midway of a limited range, in coordination with the area of the outlet hole and the load per inch characteristics of the spring to compensate for this force. A constant flow rate, within the limited design range, can thereby be maintained over a wide range of pressure, while maintaining optimum compactness of design for a given flow rate. No such optimum results appear to have been achieved in the prior art.